Power source protecting device

ABSTRACT

A power source protecting device comprises a power source switching unit for shutting off the power supply from an AC power source according to an open control signal, a surge voltage protecting unit for outputting the open control signal when a surge voltage occurs, a leakage current protecting unit for outputting the open control signal when a leakage current occurs, and an over-current protecting unit for outputting the open control signal according to a current value when an over-current occurs. The present invention can provides the surge voltage protection, the leakage current protection and the over current protection at the same time. In comparison with the conventional power source protecting device, the invention can provide a more compact and low cost device, and is able to provide an accurate and safe protection according to the current detection based on an energy.

[0001] This application incorporates by reference of Taiwan application Serial No. 090130266, filed Dec. 6, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates in general to a power source protecting device. More specifically, the present invention relates to a power source protecting device capable of preventing over-current, leakage current and surge current at the same time.

[0004] 2. Description of Related Art

[0005] As the technology is developed far beyond our imagination, people count on electrical appliances more and more. For example, computer, washing machine, micro-oven, air-conditioner, and refrigerator, etc., bring great convenience for people and increase their living quality. However, as the amount of the electricity used increases, the danger also increases. Generally, abnormal electrical phenomenon includes over-current, leakage current and surge current. Over-current means that the total current used for the appliances is too large, so as to cause wire to fire. The leakage current always occurs at a high humidity environment, such as the bathroom, so that the current flows through the human body to cause the electric shock, for example, a current over 8 mA generally causes the electric shock. The surge voltage means that a high voltage occurs suddenly and temporally, which causes the appliances to be damaged. Conventionally, different power source protecting devices corresponding to respective abnormal phenomenon of the power source are individually developed. For example, some extension outlets have surge voltage protection device with fuse to prevent the appliance from being damaged by the surge current. In addition, regarding the over-current protection, fuse, mechanical over-current switch, or device using circuit detector are provided. However, the conventional power source protecting device can only provide one function to solve one of the aforementioned problems. To preventing the power source from being damaged by different abnormal phenomenon, protection devices with different functions have to be purchased, so that the purchase cost increases and the difficulty for building the power source protection system also increases.

SUMMARY OF THE INVENTION

[0006] According to the foregoing description, an object of this invention is to provide a power source protecting device capable of preventing over-current, leakage current and surge voltage at the same time.

[0007] According to the object(s) mentioned above, the present invention provides a power source protecting device. The power source protecting device comprises a power source switching unit, a surge voltage protection, a leakage protection unit and an over-current protection unit. The power source switching unit is coupled to an alternating current (AC) power source, for shutting down the supply of the AC power source based on an open control signal. The surge voltage protection unit is coupled to the AC power source and the power source switching unit, for preventing the surge voltage. When the surge voltage protection unit detects the voltage of the AC power source is larger than a surge voltage threshold, the surge voltage protection unit outputs the open control signal. The leakage protection unit is coupled to the AC power source and the power source switching unit, for preventing the leakage current at the AC power source. The leakage protection unit receives a current difference between the fire line and the ground line and compares the current difference with a leakage current threshold. If the current difference between the fire line and the ground line is larger than the leakage current threshold, the open control signal is outputted. The over-current protection unit is coupled to the AC power source and the power source switching unit, for preventing an over-current at the AC power source. The over-current protection unit outputs the open control signal according to the current value or the energy output from the AC power source.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:

[0009]FIG. 1 is a block diagram of a power source protecting device according to one preferred embodiment of the present invention; and

[0010]FIG. 2 is a detail block diagram of the power source protecting device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0011]FIG. 1 is a block diagram of a power source protecting device according to one preferred embodiment of the present invention. Referring to FIG. 1, a power source protecting device 100 is coupled to an AC power source 101 and an electronic apparatus 180 for shutting off the AC power source 101 to protect the electronic apparatus 180 when an abnormal power supply occurs. The power source protecting device 100 comprises a power source switching unit 110, a surge voltage protecting unit 120, a leakage current protecting unit 140, and an over-current protecting unit 160. The power source switching unit 110 is coupled to the AC power source 101. When the power source switching unit 110 receives an open control signal C, the power source switching unit 110 is switched off and the AC power source 101 is disconnected to the electronic apparatus 180. That is, the power supply of the AC power source 101 is shut off and no power is supplied to the electronic apparatus 180.

[0012] The surge voltage protecting unit 120 is coupled to the AC power source 101 to prevent the surge voltage from damaging the electronic apparatus 180. The surge voltage protecting unit 120 is further coupled to the power source switching unit 110 to detect the voltage of the AC power source 101. After comparing the voltage of the AC power source 101 with a surge voltage threshold Sth, the open control signal C is outputted when the voltage of the AC power source 101 is greater than the surge voltage threshold Sth.

[0013] The leakage current protecting unit 140 is coupled to the AC power source 101 and the power source switching unit 110 to prevent the leakage current at the AC power source 101. The leakage current protecting unit 140 receives the current values flowing through a fire line F and a ground line G. If the difference between the current values flowing through the fire line F and the ground line G is greater than a leakage current threshold Lth, the open control signal C is outputted.

[0014] The over-current protecting unit 100 is coupled to the AC power source 101 and the power source switching unit 110. When over currents generated from the AC power source 101, the open control signal C is outputted.

[0015]FIG. 2 is a detail block diagram of the power source protecting device 100. The AC power source 101 comprises the fire line F and the ground line G. The surge voltage protecting unit 120 comprises a voltage sensor 122, a noise filter 124, and a surge voltage comparator 126. The voltage sensor 122 is coupled to the AC power source 101 for receiving the voltage of the AC power source 101 which is then passed to the noise filter 124. The noises of the signal indicating the voltage of the AC power source 101 is filtered and is converted to a voltage signal Ds. The surge voltage comparator 126 is used to compare the voltage signal Ds with the surge voltage threshold Sth. If the voltage signal Ds is larger than the surge voltage threshold Sth, the open control signal C is outputted. The surge voltage comparator 126 can be a digital comparator, for example.

[0016] The leakage current protecting unit 140 comprises a current sensor 142, a noise filter 144 and a leakage current comparator 146. The current sensor 142 is coupled to the AC power source 101 for receiving the current values flowing through the fire line F and the ground line G. Then, the difference between the current values flowing through the fire line F and the ground line G is amplified and transmitted to the noise filter 144. The noise filter 144 filters the noises and then outputs a leakage current amplifying signal A. The leakage current comparator 146 is coupled to the power source switching unit 110 for comparing the leakage current amplifying signal A with the leakage current threshold Lth. If the leakage current amplifying signal A is larger than the leakage current threshold Lth, the open control signal C is outputted. In general, human body will be electric shocked if the current is between 8 mA and 22 mA. Therefore, the leakage current threshold Lth can be set between these values. Besides, the leakage current comparator 146 can be an analog comparator, for example.

[0017] The over-current protecting unit 160 comprises an instantly breaking element, a short-time abnormal control element and a long-time overload control element. For a general wire, such as the wire having a current rating of 10A, when the instantly breaking element detects an extremely large current, for example larger than 20A, a breaking protection process is immediately executed. The instantly breaking element comprises a current sensor 162, an analog/digital converter 164, a noise filter 168 and an instant comparator 174. The current sensor 162 is coupled to the AC powers source 101 for receiving the current value from the AC power source 101 that is then converted into a digital signal Da by the analog/digital converter 164. The noise filter 168 filters noises out of the digital signal Da and then outputs a digital signal Da' that will be fed into the instant comparator 174. The instant comparator 174 compares the digital signal Da' with an instant threshold OI. If the digital signal Da' is larger than the instant threshold OI, the open control signal C is outputted. The instant threshold OI can be set about 20A, for example.

[0018] Current between 10A and 20A will not cause danger in a very short-time. Therefore, a short-time abnormal or a long-time overload protection can be used based upon the energy accumulated within a certain time. For example, the tolerance time for a current of 12A is larger than the tolerance time for a current of 18A. Accordingly, when determining whether to shut off the power source, better protection effect can be achieved by determining regard to the accumulated energy released within a certain time. In this embodiment, the short-time abnormal control element and the long-time overload control element are used to calculate respectively the energy released within the short-time interval Ts and the long-time interval T1, by which whether the breaking protection is performed or not is determined. However, the time intervals are not restricted by the above two kinds.

[0019] The short-time abnormal control element comprises a current sensor 162, an analog/digital converter 164, and integrator 166, an abnormal time calculator 172 and an abnormal amplifier 176. The integrator 166 receives the digital signal Da to integrate the square of the digital signal Da with respect to a time interval Δt, so as to output an energy signal E. The abnormal time calculator 172 receives the energy signal E to calculate and output an accumulated energy SI in a short-time interval Ts. The abnormal comparator 176 compares the accumulated energy SI with an abnormal threshold OS. If the accumulated energy SI is larger than the abnormal threshold OS, the open control signal C is generated. The short-time interval can be about 3 to 5 seconds, for example.

[0020] The long-time overload control element comprises a current sensor 162, an analog/digital converter 164, an integrator 166, an over-current time calculator 170 and an over-current comparator 178. The over-current time calculator 170 receives the energy signal E to calculate and output an energy LI accumulated within a long-time interval T1. The over-current comparator 178 is used to compare the energy LI and the over-current threshold OL. If the energy LI is larger than the over-current threshold OL, the open control signal C is outputted. The long-time interval T1 is about 3 to 5 minutes. In the present embodiment, the current sensor 162 and the digital/analog converter 164 are shared by the instantly breaking element, the short-time abnormal control element and the long-time overload control element. The integrator 166 is shared by the short-time abnormal control element and the long-time overload control element.

[0021] Conventionally, in order to provide the surge voltage protection, the leakage current protection and the over-current protection, three different power source protecting devices have to be provided. However, in the present invention, the three power source protecting devices are integrated, so that the volume can be reduced and the cost is reduced. Furthermore, the over-current protecting unit can determine whether abnormal phenomenon occurs according to the energy consumption within a time interval, and therefore, the power source can be protected by a safer manner.

[0022] According to the embodiment described above, the power source protecting device can provide the surge voltage protection, the leakage current protection and the over-current protection at the same time. In comparison with the conventional structure, the cost is further reduced and the over-current is detected based on the accumulated energy to provide an accurate and safe protection.

[0023] While the present invention has been described with a preferred embodiment, this description is not intended to limit our invention. Various modifications of the embodiment will be apparent to those skilled in the art. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention. 

What is claimed is:
 1. A power source protecting device, coupled to an alternating current (AC) power source having a fire line and a ground line, the power source protecting device comprising: a power source switching unit, coupled to the AC power source, for shutting off the AC power source according to an open control signal; a leakage current protecting unit, coupled to the AC power source and the power source switching unit, for preventing a leakage current at the AC power source, wherein the leakage current protecting unit receives current values flowing through the fire line and the ground line and compares the difference between the current values with a leakage current threshold, and wherein if the difference between the current values is greater than the leakage current threshold, the open control signal is outputted; and a over-current protecting unit, coupled to the AC power source and the power source switching unit, for preventing an over-current at the AC power source, wherein the over-current protecting unit determines whether the open control signal is outputted or not according to a current value from the AC power source or an energy from an output of the AC power source.
 2. The power source protecting device of claim 1, wherein the over-current protecting unit comprises an instantly breaking element, when the instantly breaking element detects that a current of the AC power source is larger than an instant threshold, the open control signal is outputted, and the instantly breaking element comprises: a current sensor, coupled to the AC power source, for outputting a first current value of the AC power source; a digital/analog converter, for receiving and converting the first current value into a digital signal; and an instant comparator, coupled to the digital/analog converter and the power source switching unit, for comparing the digital signal with the instant threshold, wherein if the digital signal is larger than the instant threshold, the open control signal is output.
 3. The power source protecting device of claim 2, wherein the instantly breaking element further comprises a noise filter for filtering noises of the digital signal.
 4. The power source protecting device of claim 1, wherein the over-current protecting unit comprises a short-time abnormal control element, when the short-time abnormal control element detects that an output energy of the AC power source released within a short-time interval is larger than an abnormal threshold, the open control signal is outputted, and wherein the short-time abnormal control element comprises: a current sensor, coupled to the AC power source, for outputting a first current value of the AC power source; a digital/analog converter, for receiving and converting the first current value into a digital signal; an integrator, for receiving the digital signal to integrate a square of the digital signal within a time interval, to obtain an energy signal; an abnormal time calculator, for receiving the energy signal to calculate a short-time energy accumulated within a short-time interval; and an abnormal comparator, for comparing the short-time energy with the abnormal threshold, wherein if the short-time energy is larger than the abnormal threshold, the open control signal is outputted.
 5. The power source protecting device of claim 1, wherein the over-current protecting unit further comprises a long-time overload control element, when the long-time overload control element detects that an output energy of the AC power source within a long-time interval is larger than an over-current threshold, the open control signal is outputted, and wherein the long-time overload control element comprises: a current sensor, coupled to the AC power source, for outputting a first current value of the AC power source; a digital/analog converter, for receiving and converting the first current value into a digital signal; an integrator, for receiving the digital signal to integrate a square of the digital signal within a time interval, to obtain an energy signal; an over-current time calculator, for receiving the energy signal to calculate a long-time energy accumulated within a long-time interval; and an over-current comparator, for comparing the long-time energy with the over-current threshold, wherein if the long-time energy is larger than the long threshold, the open control signal is outputted.
 6. The power source protecting device of claim 1, wherein the over-current protecting unit comprises: a current sensor, coupled to the AC power source, for outputting a second current value according to a difference between the current values flowing the fire line and the ground line of the AC power source; and a leakage current comparator, for receiving the second current value, wherein if the second current value is larger than the leakage current threshold, the open control signal is outputted.
 7. The power source protecting device of claim 6, wherein the leakage current protecting unit further comprises a noise filter for filtering noises of the second current value.
 8. The power source protecting device of claim 1, further comprising: a surge voltage protecting unit, coupled to the AC power source and the power source switching unit, for preventing a surge voltage, and wherein the surge voltage protecting unit comprises: a voltage sensor, for receiving and then converting a voltage of the AC power source into a voltage signal; and a surge voltage comparator, for receiving the voltage signal and a surge voltage threshold, and wherein if the voltage signal is larger than the surge voltage threshold, the open control signal is outputted.
 9. The power source protecting device of claim 8, wherein the surge voltage protecting unit further comprises a noise filter for filtering noises of the voltage signal.
 10. A power source protecting device, coupled to an AC power source with a fire line and a ground line, the AC power source protecting device comprising: a power source switching unit, coupled to the AC power source, for shutting off the AC power source according to an open control signal; a surge voltage protecting unit, coupled to the AC power source and the power source switching unit, for preventing a surge voltage; a leakage current protecting unit, coupled to the AC power source and the power source switching unit, for preventing a leakage current at the AC power source, wherein the leakage current protecting unit receives current values flowing through the fire line and the ground line and compares the difference between the current values with a leakage current threshold, and wherein if the difference between the current values is greater than the leakage current threshold, the open control signal is outputted; and a over-current protecting unit, coupled to the AC power source and the power source switching unit, for preventing an over-current at the AC power source, wherein the over-current protecting unit determines whether the open control signal is outputted or not according to a current value from the AC power source or an energy from an output of the AC power source.
 11. The power source protecting device of claim 10, wherein the over-current protecting unit comprises an instantly breaking element, when the instantly breaking element detects that a current of the AC power source is larger than an instant threshold, the open control signal is outputted, and the instantly breaking element comprises: a current sensor, coupled to the AC power source, for outputting a first current value of the AC power source; a digital/analog converter, for receiving and converting the first current value into a digital signal; and an instant comparator, coupled to the digital/analog converter and the power source switching unit, for comparing the digital signal with the instant threshold, wherein if the digital signal is larger than the instant threshold, the open control signal is output.
 12. The power source protecting device of claim 11, wherein the instantly breaking element further comprises a noise filter for filtering noises of the digital signal.
 13. The power source protecting device of claim 10, wherein the over-current protecting unit comprises a short-time abnormal control element, when the short-time abnormal control element detects that the output energy of the AC power source within a short-time interval is larger than an abnormal threshold, the open control signal is outputted, and wherein the short-time abnormal control element comprises: a current sensor, coupled to the AC power source, for outputting a first current value of the AC power source; a digital/analog converter, for receiving and converting the first current value into a digital signal; an integrator, for receiving the digital signal to integrate a square of the digital signal within a time interval, to obtain an energy signal; an abnormal time calculator, for receiving the energy signal to calculate a short-time energy accumulated within a short-time interval; and an abnormal comparator, for comparing the short-time energy and the abnormal threshold, wherein if the short-time energy is larger than the abnormal threshold, the open control signal is outputted.
 14. The power source protecting device of claim 10, wherein the over-current protecting unit further comprises a long-time overload control element, when the long-time overload control element detects that an output energy of the AC power source within a long-time interval is larger than an over-current threshold, the open control signal is outputted, and wherein the long-time overload control element comprises: a current sensor, coupled to the AC power source, for outputting a first current value of the AC power source; a digital/analog converter, for receiving and converting the first current value into a digital signal; an integrator, for receiving the digital signal to integrate a square of the digital signal within a time interval, to obtain an energy signal; an over-current time calculator, for receiving the energy signal to calculate a long-time energy accumulated within a long-time interval and then to output; and an over-current comparator, for comparing the long-time energy and the over-current threshold, wherein if the long-time energy is larger than the long threshold, the open control signal is outputted.
 15. The power source protecting device of claim 10, wherein the over-current protecting unit comprises: a current sensor, coupled to the AC power source, for outputting a second current value according to a current difference between the fire line and the ground line of the AC power source; and a leakage current comparator, for receiving the second current value, wherein if the second current value is larger than the leakage current threshold, the open control signal is outputted.
 16. The power source protecting device of claim 15, wherein the leakage current protecting unit further comprises a noise filter for filtering noises of the second current value.
 17. The power source protecting device of claim 10, wherein surge voltage protecting unit comprises: a voltage sensor, for receiving and then converting a voltage of the AC power source into a voltage signal; and a surge voltage comparator, for receiving the voltage signal and a surge voltage threshold, and wherein if the voltage signal is larger than the surge voltage threshold, the open control signal is outputted.
 18. The power source protecting device of claim 17, wherein the surge voltage protecting unit further comprises a noise filter for filtering noises of the voltage signal.
 19. A power source protecting device, coupled to an AC power source with a fire line and a ground line, the AC power source protecting device comprising: a power source switching unit, coupled to the AC power source, for shutting off the AC power source according to an open control signal; a surge voltage protecting unit, coupled to the AC power source and the power source switching unit, for preventing a surge voltage; and a leakage current protecting unit, coupled to the AC power source and the power source switching unit, for preventing a leakage current at the AC power source, wherein the leakage current protecting unit receives a current value flowing through the fire line and the ground line and compares the current value with a leakage current threshold, and wherein if the current difference between the current value and the leakage current threshold, the open control signal is outputted.
 20. The power source protecting device of claim 17, further comprising: a over-current protecting unit, coupled to the AC power source and the power source switching unit, for preventing an over-current at the AC power source, wherein the over-current protecting unit determines whether the open control signal is outputted or not according to a current value from the AC power source or an energy from an output of the AC power source.
 21. The power source protecting device of claim 20, wherein the over-current protecting unit comprises an instantly breaking element, when the instantly breaking element detects that a current of the AC power source is larger than an instant threshold, the open control signal is outputted, and the instantly breaking element comprises: a current sensor, coupled to the AC power source, for outputting a first current value of the AC power source; a digital/analog converter, for receiving and converting the first current value into a digital signal; and an instant comparator, coupled to the digital/analog converter and the power source switching unit, for comparing the digital signal with the instant threshold, wherein if the digital signal is larger than the instant threshold, the open control signal is output.
 22. The power source protecting device of claim 21, wherein the instantly breaking element further comprises a noise filter for filtering noises of the digital signal.
 23. The power source protecting device of claim 20, wherein the over-current protecting unit comprises a short time abnormal control element, when the short time abnormal control element detects that an output energy of the AC power source within a short-time interval is larger than an abnormal threshold, the open control signal is outputted, and wherein the short time abnormal control element comprises: a current sensor, coupled to the AC power source, for outputting a first current value of the AC power source; a digital/analog converter, for receiving and converting the first current value into a digital signal; an integrator, for receiving the digital signal to integrate a square of the digital signal within a time interval, to obtain an energy signal; an abnormal time calculator, for receiving the energy signal to calculate a short-time energy accumulated within a short-time interval and then to output; and an abnormal comparator, for comparing the short-time energy and the abnormal threshold, wherein if the short-time energy is larger than the abnormal threshold, the open control signal is outputted.
 24. The power source protecting device of claim 20, wherein the over-current protecting unit further comprises a long-time overload control element, when the long-time overload control element detects that an output energy of the AC power source within a long-time interval is larger than an over-current threshold, the open control signal is outputted, and wherein the long-time overload control element comprises: a current sensor, coupled to the AC power source, for outputting a first current value of the AC power source; a digital/analog converter, for receiving and converting the first current value into a digital signal; an integrator, for receiving the digital signal to integrate a square of the digital signal within a time interval, to obtain an energy signal; an over-current time calculator, for receiving the energy signal to calculate a long-time energy accumulated within a long-time interval; and an over-current comparator, for comparing the long-time energy and the over-current threshold, wherein if the long-time energy is larger than the long threshold, the open control signal is outputted.
 25. The power source protecting device of claim 19, wherein the over-current protecting unit comprises: a current sensor, coupled to the AC power source, for outputting a second current value according to a current difference between the fire line and the ground line of the AC power source; and a leakage current comparator, for receiving the second current value, wherein if the second current value is larger than the leakage current threshold, the open control signal is outputted.
 26. The power source protecting device of claim 25, wherein the leakage current protecting unit further comprises a noise filter for filtering noises of the second current value.
 27. The power source protecting device of claim 19, wherein the surge voltage protecting unit comprises: a voltage sensor, for receiving and then converting a voltage of the AC power source into a voltage signal; and a surge voltage comparator, for receiving the voltage signal and a surge voltage threshold, and wherein if the voltage signal is larger than the surge voltage threshold, the open control signal is outputted.
 28. The power source protecting device of claim 27, wherein the surge voltage protecting unit further comprises a noise filter for filtering noises of the voltage signal.
 29. A power source protecting device, coupled to an AC power source with a fire line and a ground line, the AC power source protecting device comprising: a power source switching unit, coupled to the AC power source, for shutting off the AC power source according to an open control signal; a surge voltage protecting unit, coupled to the AC power source and the power source switching unit, for preventing a surge voltage; and a over-current protecting unit, coupled to the AC power source and the power source switching unit, for preventing an over-current at the AC power source, wherein the over-current protecting unit determines whether the open control signal is outputted or not according to a current value from the AC power source or an energy from an output of the AC power source.
 30. The power source protecting device of claim 29, wherein the over-current protecting unit comprises an instantly breaking element, when the instantly breaking element detects that a current of the AC power source is larger than an instant threshold, the open control signal is outputted, and the instantly breaking element comprises: a current sensor, coupled to the AC power source, for outputting a first current value of the AC power source; a digital/analog converter, for receiving and converting the first current value into a digital signal; and an instant comparator, coupled to the digital/analog converter and the power source switching unit, for comparing the digital signal with the instant threshold, wherein if the digital signal is larger than the instant threshold, the open control signal is output.
 31. The power source protecting device of claim 30, wherein the instantly breaking element further comprises a noise filter for filtering noises of the digital signal.
 32. The power source protecting device of claim 29, wherein the over-current protecting unit comprises a short time abnormal control element, when the short time abnormal control element detects that an output energy of the AC power source within a short-time interval is larger than an abnormal threshold, the open control signal is outputted, and wherein the short time abnormal control element comprises: a current sensor, coupled to the AC power source, for outputting a first current value of the AC power source; a digital/analog converter, for receiving and converting the first current value into a digital signal; an integrator, for receiving the digital signal to integrate a square of the digital signal within a time interval, to obtain an energy signal; an abnormal time calculator, for receiving the energy signal to calculate a short-time energy accumulated within a short-time interval and then to output; and an abnormal comparator, for comparing the short-time energy and the abnormal threshold, wherein if the short-time energy is larger than the abnormal threshold, the open control signal is outputted.
 33. The power source protecting device of claim 29, wherein the over-current protecting unit further comprises a long-time overload control element, when the long-time overload control element detects that an output energy of the AC power source within a long-time interval is larger than an over-current threshold, the open control signal is outputted, and wherein the long-time overload control element comprises: a current sensor, coupled to the AC power source, for outputting a first current value of the AC power source; a digital/analog converter, for receiving and converting the first current value into a digital signal; an integrator, for receiving the digital signal to integrate a square of the digital signal within a time interval, to obtain an energy signal; an over-current time calculator, for receiving the energy signal to calculate a long-time energy accumulated within a long-time interval and then to output; and an over-current comparator, for comparing the long-time energy and the over-current threshold, wherein if the long-time energy is larger than the long threshold, the open control signal is outputted.
 34. The power source protecting device of claim 29, further comprising a over-current protecting unit, coupled to the AC power source and the power source switching unit, for preventing an over-current at the AC power source, wherein the over-current protecting unit determines whether the open control signal is outputted or not according to a current value from the AC power source or an energy from an output of the AC power source, and wherein the over-current protecting unit comprises: a current sensor, coupled to the AC power source, for outputting a second current value according to a current difference between the fire line and the ground line of the AC power source; and a leakage current comparator, for receiving the second current value, wherein if the second current value is larger than the leakage current threshold, the open control signal is outputted.
 35. The power source protecting device of claim 34, wherein the leakage current protecting unit further comprises a noise filter for filtering noises of the second current value.
 36. The power source protecting device of claim 29, wherein the surge voltage protecting unit comprises: a voltage sensor, for receiving and then converting a voltage of the AC power source into a voltage signal; and a surge voltage comparator, for receiving the voltage signal and a surge voltage threshold, and wherein if the voltage signal is larger than the surge voltage threshold, the open control signal is outputted.
 37. The power source protecting device of claim 36, wherein the surge voltage protecting unit further comprises a noise filter for filtering noises of the voltage signal. 